The Cable Plant
The Open Systems Interconnection (OSI) reference model of the International Standards Organization (ISO — Geneva, Switzerland) divides the functions involved in the exchange of information between computer systems into seven layers, with the physical layer at the bottom and the application layer at the top. The physical layer, as its name implies, comprises the cable, connectors, and other passive components included in the cable plant that link computers and other networked end-user devices to the hubs, bridges, routers, and other active devices in the local area network (LAN). The basic component of any cable plant is clearly the cable itself. Although there are only four major cabling media — coaxial, shielded or screened twisted-pair, unshielded twisted-pair, and optical fiber — there are variations within each medium to serve the many tasks that cable is called upon to perform. Most cable plants need a generic cable-grouping or management device, a need which is usually filled by the plastic cable tie.